According to WHO statistics, as many as 170 million people worldwide are infected by hepatitis C virus (HCV), a viral infection of the liver. 75 to 85% of persons infected with HCV progress to chronic infection, approximately 20% of these cases develop complications of chronic hepatitis C, including cirrhosis of the liver or hepatocellular carcinoma after 20 years of infection. The current recommended treatment for HCV infections is a combination of interferon and ribavirin drugs, however the treatment is not effective in all cases and the liver transplantation is indicated in hepatitis C-related end-stage liver disease. At present, there is no vaccine available to prevent HCV infection, therefore all precautions to avoid infection must be taken.
Thus, patient care, as well as the prevention of transmission of Hepatitis C Virus (HCV) by blood and blood products or by close personal contact requires extreme vigilance using sensitive detection assays. This creates a need for specific methods for screening and identifying carriers of HCV and HCV-contaminated blood or blood products. Serological determination of HCV exposure relies on the detection of HCV present in human blood plasma or sera. This can be accomplished by detection of distinct structural and non-structural proteins encoded by the virus or alternatively by detection of antibodies to HCV.
After exposure to the HCV pathogen, there is initially no evidence of viral presence, i.e. no detectable viral RNA or serology markers. This is referred to as the “window period” (WP). Generally, after 10 days following exposure to HCV, viral RNA can be detected while anti-HCV antibodies become detectable approximately 70 days later (Busch M P and Dodd R Y, Transfusion 40(10): 1157-1160, 2000). Prevention of HCV infection spread it is ever more important to have reliable blood-screening tests that are designed to narrow the detection window.
There are numerous methods for the detection of HCV infection based on serological screening of the blood for detecting the presence of HCV core antigen or antibodies against HCV polypeptides in patient serum or plasma. It has been noted that the assays directed at detection of HCV core antigen assay detects HCV infection between 40 to 50 days earlier than the HCV screening based on antibody screening assays. HCV core protein is a structural protein of HCV comprising the first 191 amino acids of the polyprotein and that forms the internal viral coat encapsidating the genomic RNA. Two different types of serologic assays have been developed which permit detection of HCV core antigens in serum. One assay format detects HCV core antigens in subjects prior to seroconversion and is utilized in screening blood donors, while the other assay format detects core antigens only in hepatitis C patients, regardless of their HCV antibody status, and is utilized in clinical laboratories to diagnose exposure to HCV or to monitor antiviral therapy.
Typically however, the HCV core antigen blood screening assays only detect core antigen at pre-seroconversion or early post-seroconversion phase. Furthermore, HCV core antigen assays are unable to detect core antigen when the antigen forms immune-complexes with anti-core antibodies in the late seroconversion phase. This creates a need for a serological assay that can detect HCV core antigen in the pre-seroconversion phase as well as anti-HCV antibodies in the seroconversion phase, thus narrowing the WP significantly.
The utility of such combination HCV screening assays is significant as such assays will be a significant improvement over the current serology blood screening method with respect to narrowing the WP. However, one of the challenges to the successful antigen antibody combined assay is to select appropriate antigens and antibodies for performing such assays. The present invention addresses this need.